Couscous

ABSTRACT

A shelf-storable new and improved couscous food product satisfying traditional couscous granular mouthfeel is made by extruding a wheat-based doughy mass and cutting the extrudate into particles of uniform couscous size (i.e., between about 0.85 and about 2.5 mm. mesh). When examined under a magnification of 12 times, the new particles, although lacking the agglomeration structure of traditional couscous, have a mouthfeel structure characterized by (i) substantially smooth surfaces on the exterior thereof and (ii) angularly projecting edges on the exterior thereof. Further, the particles are substantially translucent, have a Water Absorption Index greater than 4.7, and have a substantially uniform and dense extrusion compacted composition comprised essentially of the starches and gluten-forming proteins in a blend of durum wheat flour or middlings or semolina and an optional content of flours or middlings or farinas of cereal grains other than durum wheat. At least about 80% of the dry solids weight of the starches in the product are gelatinized. The product is quickly hydratable in preparing it for consumption.

BACKGROUND OF THE INVENTION

This invention relates to the food product called couscous andparticularly to a new and improved method for making couscous, to a newand improved couscous food product, and to speedy methods of preparingthe new couscous product for consumption.

Couscous appears to be unique among cereal grain food products. It isdistinguished by the special way it can be and traditionally has beenprepared for consumption, namely by a series of simple hydrating andsteaming steps. Generally, the steaming of the product to an ediblecondition is accomplished in a couscoussiere.

The traditional method for making couscous has been by mixing water withdurum wheat semolina in a gissa or large wooden dish, then rubbing themixture between the palms of one's hands to form agglomerates or smallirregularly shaped granules, screening the granules to proper size,followed by steam precooking of the granules, and finally sun-dryingthose of the proper size. Sun-dried couscous has a long shelf life.

Until recently, the traditional method has been the only known methodfor making couscous. Credit goes to the Buhler company of Uzwil,Switzerland for successfully developing a method for the commercialproduction of couscous and for setting up the first commercialproduction facility in Sfax, Tunisia in 1979. As in the traditionalmethod, the first step of the known commercial method is that ofblending water and semolina until optimum agglomeration or granuleformation is achieved. This is accomplished without forming the semolinainto a unitary doughy mass. A mechanical mixer such as a paddle mixer isused for this step and the mixing takes about 3 minutes to providegranules of a moisture content of about 30-35%.

The next step of the known commercial method involves feeding thecoarse, irregularly shaped and random-sized moist granules into adetacher where the granules of oversize are reduced and those of propersize are strengthened and shaped to form the couscous agglomerates. Thisstep takes about 7 minutes.

Thereafter wet sifting may be done to separate undesired fines andoversized particles from the proper size range for the agglomerates.Fines are recycled back to the beginning mixing step and oversizedagglomerates are routed back through the detacher.

Next the couscous agglomerates are passed on a conveyor belt through asteam cooking operation. This steaming step takes about 8 minutes at atemperature of about 180° C. The moisture of the couscous product iselevated to about 37% by weight by the time the product exits thesteaming operation. In this steaming step, approximately 55 or 60% byweight of the starch is gelatinized.

The agglomerates are then dried in climate-controlled dryers. Forexample, a predrying stage may take 2 hours at 65° C. and a main dryingstage may take 41/2 hours at 55° C. Drying is conducted until theproduct moisture is reduced below 13%, preferably to 10-12%. The driedproduct is then cooled back to ambient conditions and sifted intooversized conglomerates, fine, medium, and coarse couscous, andundersized granules. Oversized agglomerates are passed through a rollermill and the resulting fraction is resifted. Undersized particles aremetered into the beginning mixing step.

Couscous is a wheat-based particulate product that gives a granularmouthfeel. The proper size range for its dried particles is from about0.85 to about 2.5 millimeter mesh. The particles of a specific couscousproduct should not vary more than about 1 mm mesh, preferably not morethan about 0.5 mm mesh, between the largest and smallest Uniformity ofsize is a mark of quality for couscous and has not been easily achievedusing known methods of manufacture. Particles lacking uniformity ofshape and size result in irregular cooking quality and unsatisfactorymouthfeel. The required property of granular mouthfeel further meansthat the particles must remain separate and not stick together when theyare rehydrated and cooked (as by steaming) for consumption. Cooking withsauces or moisture should soften the particles but not so greatly thatthey exhibit no resistance to the bite. Chewing of the particles shouldshear them, that is, subdivide them into smaller and smaller particles.The chewed particles should not give a brittle or rubbery or sticky orpasty or gummy feeling. The traditional granular mouthfeel associatedwith agglomerates is critical.

The major problems associated with the known commercial technique formanufacturing couscous have centered on quality and particularly theexpense of getting quality. There is the initial expense caused by usingdurum semolina and avoiding the more economical durum flour as astarting material, the extra expense involved in special reworking ofpowdery fines and crushing oversized particles, the base expense for theextensive capital equipment as well as the relatively large factoryspace to accommodate it, and the unrelenting expenses associated withthe several costly handling steps.

The thrust of this invention takes the couscous art in an entirelydifferent direction from that which it has taken in the past. In thisregard, insofar as is known, no one has heretofore proposed a method forthe manufacture of couscous that would consistently yield particles ofproper size and of relatively uniform size and shape, without anysignificant powdery fines and without any significant oversizedparticles. It further appears that no one in the past has had theslightest inkling that substantially uniformly shaped and smoothsurfaced particles could satisfy couscous criteria and in fact give thetraditional couscous granular mouthfeel heretofore associated only withthe irregularly shaped agglomerated prior art particles. It stillfurther appears that no one ever conceived that uniformly shapedparticles could possess still other couscous sought-for attributes suchas desired firmness associated with mouthfeel, desired avoidance ofobjectionable stickiness, and desired quick rehydration and reduced timeof steam cooking for consumption--plus no significant loss of color andeven an enhancement of the yellowness for durum couscous (but color ishighly dependent on the composition of the starting material). It is inthis uncharted new direction that the couscous art is taken by thisinvention.

SUMMARY OF THE INVENTION

The present invention results from the discovery, despite years and evencenturies of couscous practices requiring the contrary, that couscouscan in fact be made by extrusion processing of a doughy mass.

The invention provides a shelf-storable improved couscous food productsatisfying traditional couscous granular mouthfeel. The product consistsessentially of non-sticky free-flowing wheat-based particles having asize between about 0.85 and about 2.5 mm mesh, and having a moisturecontent below about 13% by weight. It is relatively quickly hydratableand steam cooked without loss of its particulate integrity. It isparticularly characterized by the fact that its particles aresubstantially translucent, have a Water Absorption Index greater than4.7, and have a substantially uniform and dense extrusion-compactedcomposition. The composition is comprised essentially of the starchesand gluten-forming proteins in a blend of, by dry solids weight, atleast about 65% up to 100% of durum wheat flour or middlings or semolinaand about 35% down to 0% of flours or middlings or farinas of cerealgrains other than durum wheat. At least about 80% of the dry solidsweight of the starches is gelatinized. The particles are furthercharacterized by having, when examined under a magnification of 12times, (i) substantially smooth surfaces on the exterior thereof and(ii) angularly projecting edges on the exterior thereof.

Preferred particles are such that their substantially smooth exteriorsurfaces include opposing surfaces in generally parallel relationshipand include side surfaces extending between and angularly connected atabout 90° to the opposing surfaces. The angularly projecting edges ofsuch particles comprise the edges formed at the angular connectionsbetween the side surfaces and the opposing surfaces. Preferred particlesalso exhibit their shortest linear dimension in a directionsubstantially perpendicular to the opposing surfaces. The ideal couscousproduct of the invention has particles of substantially the same sizeand shape.

One method of preparing the new product for consumption consistsessentially of adding the product to boiling water and simmering theproduct in the boiling water for 2 minutes, followed by allowing theproduct to stand in the water without additional heating for 2 minutes.

Another method of preparing the new product for consumption consistsessentially of hydrating the product in a single hydration step usingsufficient water at 25° C. for 2 to 6 minutes for the product toincrease its weight at least to 180% of its original weight by absorbingthe water, and then steaming the hydrated product for up to 3 to 4minutes with steam at 90° C. or higher.

The improved method for making this new couscous food product is anextrusion method. A major step in conducting the method is that ofextruding a cooked mixture of wheat-based composition and watermaintained under an elevated temperature between about 70° C. and 100°C. and a pressure from about 13 bar up to about 41 bar and a moisturecontent of at least 25% but not over 45% by weight through an extrusiondie having openings of substantially uniform size within the size limitsfrom about 0.5 square millimeters up to about 7 square millimeters. Thewheat-based composition is comprised essentially of the starches andgluten-forming proteins in a blend of, by dry solids weight, at leastabout 65% up to 100% of durum wheat flour or middlings or semolina andabout 35% down to 0% of flours or middlings or farinas of cereal grainsother than durum wheat. The extrudate of the die is cut and then driedunder elevated temperatures to a moisture content below 13% by weight.

Preferably the extrusion of the cooked mixture is conducted at a linearextrusion rate in excess of 1,200 mm/min. Also, the extrusion dieemployed preferably has a substantially flat outer face and the cuttingsurface of the extrudate is conducted at a cutting rate in excess of 500cuts per minute across the face of the die. The linear extrusion rateand the cutting rate are preferably such that the extrudate is cut intoparticles having cut lengths with parallel surfaces spaced apart atleast about 0.5 mm up to about 2.5 mm.

Steps of the method preliminary to the extrusion step comprise:

a) Forming a mixture of the wheat-based composition and water in apreconditioner so as to have a moisture content between about 20% and30% by weight and an elevated temperature up to but not over 100° C.,the mixture having a dwell time of mixing in the preconditioner betweenabout 30 seconds and 2 minutes;

b) Passing the mixture from the preconditioner into the barrel of anextruder having a cooking zone, venting zone, forming zone,stabilization zone, and the aforesaid extrusion die, and having arotatable screw in the cooking, venting, and forming zones;

c) Rotating the screw of the extruder to advance the mixturesequentially through the cooking, venting, and forming zones and out ofthe barrel into the stabilization zone and through the extrusion die,the dwell time for the mixture to pass through all zones of the extruderand out the extrusion die being between about 1.0 and 2.5 minutes;

d) Raising the temperature of the mixture to a temperature in excess of90° C. up to about 130° C. and increasing its moisture content to alevel in excess of 30% by weight up to about 50% by weight in thecooking zone;

e) Reducing the moisture content of the mixture by removing moisturetherefrom in the venting zone but maintaining the moisture content ofthe mixture at a level in excess of 25% by weight and not over 45% byweight as the mixture leaves the venting zone;

f) Increasing the pressure on the mixture and maintaining itstemperature between about 70° C. and 100° C. as it is advanced throughthe forming zone, but dropping the pressure on the mixture in thestabilization zone, the pressure in the forming zone being at least 13bar higher than the pressure in the stabilization zone, the pressure inthe stabilization zone being the pressure under which the cooked mixtureis extruded through the extrusion die.

The preferred method also contemplates forcing the mixture through aconstriction between the forming zone and stabilization zone.

Still other features and benefits and advantages of the invention willbe evident as this description proceeds.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a photograph of preferred couscous particles of this inventionshowing them magnified 12 times;

FIG. 1a is a schematic enlarged perspective view of a preferred shapefor a couscous particle of the invention;

FIGS. 2 and 3 are photographs illustrative of agglomerated couscousparticles formed according to prior art, namely hand-made andmachine-made agglomerations, respectively, each photograph showing theparticles magnified 12 times; and

FIG. 4 is a schematic illustration of suitable apparatus elements forconducting the new method of making couscous according to the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The new method for making couscous does not require the specificapparatus here discussed. Nevertheless, the method is better understoodby reference to a useful apparatus for conducting it.

Referring to FIG. 4, the preconditioner or conditioning cylinder 10 hasan entrance 11 and an exit 12 and preferably contains twin laterallyjuxtaposed counter-rotating shafts 13 (only one schematicallyillustrated) equipped with paddles 14 oriented at various pitches toadvance the raw material through the preconditioner from entrance toexit and to provide a controlled dwell time for the material in thepreconditioner as the material is being mixed. The preconditioner alsoincludes a water conduit 15 with metering means for introduction ofwater near its entrance, as well as steam injection ports 16 withmetering means for controlled injection of steam along the bottom of theinterior of the preconditioner.

The paddles 14 preferably are in three different groups. At the entranceend 11 the paddles are oriented so that they forcibly convey thematerial forward to the exit 12. In the middle portion, the paddlespreferably are at a neutral angle and therefore do not themselveseffectively function to move material through the preconditioner. Theyact to mix the material with the steam and water. The paddles near theexit portion 12 are preferably located at an angle or pitch such thatthey relatively tend to push or compact material in a reverse direction(back toward entrance) as the material is being forced forward throughthe preconditioner by the build up caused by the forward-motion paddlesnear the entrance end. The pitch of these paddles and the shaft rpm areadjusted so as to achieve the desired dwell time of between about 30seconds and 2.5 minutes in the preconditioner.

Material exiting the preconditioner is fed into the barrel 21 of anextruder 20. The entrance 22 of extruder 20 may be joined to the exit ofthe preconditioner, if desired.

A useful extruder barrel is known in the United States under the tradename "Wenger TX-52" (screw elements of 52-mm diameter), and is describedwith a process for its use in Wenget et al. U.S. Pat. No. 4,763,569 ofAug. 16, 1988, here incorporated by reference. An extruder barrel 21having a length to diameter ratio of about 25:1 is useful for practicingthis invention. As illustrated in FIG. 4, it suitably includes nine headelements numbered 1 through 9, each about 15 cm. in length.

The composite barrel 21 has several zones, namely a cooking zone X, aventing zone Y, and a forming zone Z. The complete extruder 20, asstyled for this invention, also has a special stabilization zone M andfinally terminates at its exit end in an extrusion die 23, which ispreferably horizontally oriented. Within the barrel portion of theextruder, and extending through the cooking, venting and forming zones,is a rotatable shaft 41 carrying rotatable screw propulsion means 24 formoving material not only through the barrel 21 (in which screwpropulsion is located), but also all the way through stabilization zoneM (where no screw propulsion is needed) to the exit die 23. Althoughsingle screw extruders may be employed successfully for the practice ofthe invention, the most preferred extruders are comprised of twinintermeshing co-rotating screw elements such as employed in the "WengerTX-52".

The portion of the shaft 41 extending through the cooking zone (headelements 3, 4 and 5) is preferably equipped with several reverse pitchshearlocks, that is, contoured bodies for effecting shearing action onthe mixture being worked.

Each of the head elements 1 through 9 has a jacket 40 through which aheating or cooling fluid is circulated to control the head elementtemperature. Of course, head element temperatures can be controlled byother means, such as, for example, by electricity.

A water conduit 25 into head 2 is for adding water to the mixture, andsteam entrances 26 and 27 into heads 3 and 4 are for injecting themixture with steam.

Head 6 is provided with a vent stack 28 for the escape of moisture fromthe mixture, primarily in the form of steam vapors. To facilitate rapidremoval of vapors, a negative pressure of 0.3 bar gauge to 0.5 bar gaugeis drawn on the exit vent 29. An auger 30 or similar device is employedto retain or return material that expands out of barrel 21 into thestack 28 back into the extruder barrel 21 while the negative pressure isapplied.

The forming zone Z is next and terminates at the end of the extruderbarrel 21 where a choke or constriction 31 for practicing the inventionis located. The constriction 31 used in conducting experiments of thisinvention had two openings of about 6 mm diameter--one at the end ofeach screw of a twin screw extruder--with both openings emptying to acenter channel of about 9.5 mm diameter which in turn emptied into thestabilization zone M.

The stabilization zone M is defined by a continuation housing 32. Thehousing 32 used for experiments had a length of about 25 cm and adiameter of about 7.5 cm. The stabilization zone continues through theelbow 33 which effects a change of direction.

A screen 34 (e.g., 0.6 mm mesh or 30 mesh U.S. Standard) may desirablybe employed at the interior surface of die 23 to improve uniformity offlow across the die and to screen out foreign particles from the doughmass, thereby saving the die 23 from unnecessary wear.

The die 23 is preferably oriented in a horizontal plane for verticalpassage through the die. Dies for practicing the invention have amultiplicity of very small die openings or holes. All openings for anyone die are preferably of equal size (i.e. equal in area dimension). Theopenings may vary from about 0.5 to about 5 or 6 or possibly 7 squaremillimeters for different dies. Square or multi-sided openings may beused, but ideally, the openings are circular to give a cylindrical shapeto resulting extrusions. A vermicelli die available commercially in theUnited States as Maldari #42801 (having 1.219 mm (0.048-inch) diameteropenings) gives excellent results.

A cutter 35 such as a four blade knife is fitted flush to the outer dieface or surface and rotated at a significant speed (e.g., to provide atleast 500 cuts per minute). The cutter slices extruded material intostub-like particles which on drying give the required couscous size,namely between about 0.85 mm (possibly as short as 0.5 mm) and about 2.5mm for the extruded lengths.

The cut extrudate is dried by moving the particles through drying gassessuch as in a climate-controlled drying atmosphere. The particles mayfall or drop on a conveyor 36 and then pass through a climate-controlledatmosphere. They may be dumped from the conveyor 36 into aclimate-controlled drying atmosphere in a special space 37, or droppedfrom the die into such a space. The special space may be a stack orcolumn of rising drying gases, or a fluidized bed, or a rotary screendryer. Still other drying systems may be used for drying the particles.Countercurrent air flow systems are especially useful, but any systemeffecting relative movement between the particles and aclimate-controlled drying atmosphere can be effective.

The raw material employed as a starting material in the practice of theinvention is wheat based. The basic raw material is a milled product,and most preferably a milled product of durum wheat. Optionally, but notpreferably, a varying percentage from zero up to about 35% by dry solidsweight of the raw material may comprise the milled product (such asflour or middlings or farina) of other cereal grains. Such cereal grainsinclude wheats other than durum (e.g., hard red spring, hard red winter,soft red, soft white, etc.) plus corn or maize, millet, sorghum, milo,and any others as desired. The flour or farina of cereal grains(including durum flour or middlings or semolina) should account for atleast about 90% of the dry solids weight of the total composition, ifnot 100% of it. The flour or middlings or semolina of durum shouldalways dominate. The wheat proteins, particularly the proteins known tobe gluten-forming (and preferably the gluten-forming proteins of durum),perform an important binder-type function. They form a water-insolublenetwork or protein mass of extensible or extended character about thestarch molecules. Sometimes their performance is referred to as anenrobing of the starch. They cause starchy couscous particles of theinvention to resist breakdown and keep their particulate integrity(i.e., general shape) when they are prepared for consumption. Thegluten-forming wheat proteins preferably should at least equal andpreferably exceed about 8% of the dry solids weight of the compositionof the particles. This criterion is generally met when startingcompositions contain durum flour or middlings or semolina in an amountaccounting for at least about 65% of the dry solids weight. Of course,the protein in durum flour or middlings or semolina can vary dependingon growing conditions, but it generally exceeds 10% of the dry weight.The starches of cereal grains will generally account for at least about75% or 80% of the dry solids weight of the compositions. This criterionis generally met by using compositions comprised essentially of floursor middlings or farinas of cereal grains (i.e., 65% to 100% durum and35% to 0% other grains). Other ingredients not detracting from theessential starch and essential wheat protein may be present. Forexample, vegetable powders, fibers, and protein fractions from materialsother than cereal grains may be employed in modest quantities (generallynot over about 10% of dry solids weight) for the properties suchconstituents impart. Modest quantities of salts or inorganic componentsmay be used. Surface active agents and other processing aids are usefuland sparingly employed. While durum semolina is needed to make qualitycouscous by agglomeration methods, durum wheat flour instead of semolinamay be employed in the practice of this invention with results almostindistinguishable from results obtained using durum wheat semolina.

The yellow color highly prized for couscous results primarily from theuse of durum as starting material. Couscous made according to thepresent invention, using durum wheat flour or middlings or semolina, hasa more intense color than couscous of comparable formula made accordingto the agglomeration methods of the prior art. Substitution of varyingamounts of other cereal-based raw materials proportionally reduces thecolor intensity and can adversely affect texture and flavor.

Preliminary mixing of the raw material solids with water and steam in apreconditioner is done to give a mixture having a moisture contentbetween about 20% and 30% by weight, preferably at least about 25 or 26%up to about 28 or 29% by weight. The temperature elevation during thismixing generally will be to at least about 70° C., and preferably atleast about 80° C. to around 90° C. or more, but not over about 100° C.Starch of the mixture is partially hydrated and partially gelatinized inthis step. Preferred time for this step is between about 1.5 and 2minutes.

The mixture is then passed into the extruder barrel and the screws arerotated to advance the mixture through the cooking, venting, and formingzones and out the barrel into the stabilization zone and through theextrusion die. Dwell time in the extruder from entrance to exit throughthe die ranges between about 1.0 and 2.5 minutes, preferably betweenabout 1.5 and 2.5 minutes.

In the cooking zone, the mixture is raised to a temperature in excess of90° C. up to about 130° C. (preferably to at least about 100° C. up toabout 120° C.), and its moisture is increased to a level in excess of30% by weight (preferably in excess of 35% by weight) up to 50% byweight. Water and steam are injected at varying rates, such as, forexample, between about 4 and 10 kg/hr for water and between about 0.15and 0.30 kg/min for steam under 5 or 6 bar (80 psi). Modest shearing ofthe mixture on its way through the extruder is desirable, and isaccomplished in the cooking zone. Shearing tends to cause the mixture toform itself into a dough. While modest shearing improves product unity,integrity, and quality, excessive shearing is undesired because itcauses structural breakdown of the starch and protein network in the rawmaterial, thereby increasing the amount of undesirable soluble starch inthe final product. By conducting shear under cooking conditions ofrelatively high moisture content and elevated temperature, suchstructural breakdown is reduced and the desired amount of shearingaction is achieved.

The moisture vapors escaping from the mixture in the venting zone causea lowering of the temperature of the dough, but the lowering orreduction is not to a temperature below 70° C. The temperature is mostpreferably reduced below 100° C. but not below 80° C. in this zone. Themoisture of the dough is reduced by the vapor escape but is maintainedat a level in excess of 25% and not over 45% by weight (preferably inexcess of 30% and not over 40%) as the mixture leaves the venting zone.

Next comes the forming zone where the temperature of the dough ismaintained between about 70° C. and 100° C. (preferably between 80° C.and 100° C.) as it is subjected to increases of pressure following therelaxation of pressure in the venting zone. Pressures in the formingzone are created by the unrelenting thrust of the screw 24 in pushingthe mixture toward the constriction 31 at the end of the extruderbarrel.

The constriction functions to obstruct to some degree the movement ofmaterial from the forming zone Z into the stabilization zone M andincrease the retention time of the mixture in the extruder barrel. Italso functions to provide a pressure differential between the two zones,and to achieve a desired back pressure in the forming zone.

The constriction at 31 may be omitted with loss of its benefits. Atleast some degree of constriction is desirable and constrictions whichmaintain a pressure differential of at least about 13 bar (200 psi) upto possibly about 70 bar (1,000 psi) between the forming zone Z andstabilization zone M are preferred. The pressures applied to the mixturewithin the forming zone Z should exceed about 27 bar (400 psi).Preferred forming pressures are between about 55 bar (800 psi) and about90 bar (1,300 psi). Forming pressures as high as 95 or 102 bar (1,400 or1,500 psi) are useful. Forming pressures compress and compact the doughand enhance its development and contribute to the structural integrityor unity of the end product.

Then comes the drop in pressure as the material passes through theconstriction 31 into the stabilization zone. The material in thestabilization zone 32--held at reduced pressure compared to the formingzone--is allowed to expand. The stabilization zone 32 increases theretention time of the dough prior to extrusion and allows it to morethoroughly hydrate and achieve a higher degree of gelatinization. Dwelltime in the stabilization zone should at least exceed half the dwelltime in the forming zone. Stabilization zone pressures generally rangebetween about 13 bar (200 psi) to about 41 bar (600 psi). Preferablythey do not exceed 34 bar (500 psi). What is significant is that arelatively high moisture content (25%-45% by weight, generally 30-40%),plus a relatively high temperature (70°-100° C.), and relatively lowpressure (13-41 bar) all work together in the stabilization zone to keepthe mixture in a relatively flowable state as it is urged along and outthrough the extrusion die.

The extrudate is cut and the cut extrudate promptly subjected to dryingto a moisture content below about 13% by weight. Low moisturecontributes to long shelf storability. Drying to about 10-12% moistureby weight is useful. It for the most part is unnecessary or undesirableto incur the expense of drying to a level of moisture below about 9 or10%, although drying to lower moisture such as 6% or so is permissible.Drying is preferably done in an atmosphere of controlled humidity andtemperature. Suitable relative humidity may vary from 30% to 90%,preferably with gradual lowering of the humidity in the controlledatmosphere as drying takes place. While drying under a wide range oftemperatures is possible, the range should be limited to between 40° C.and 90° C. with the range between 70° C. and 85° C. or about 80° C. themost preferred. At about 80° C. and 30% relative humidity, drying to amoisture below 13% by weight can be accomplished in well less than 30minutes, whether the particles are on a belt or are tossed in a rotaryscreen or free-falling or suspended in a fluidized bed or floating inthe drying atmosphere. Drying involves relative movement between the cutparticles and the drying atmosphere.

The high rate of cutting extrudate is especially significant. Slice-likecutting of extrudate is effected by moving a cutter (e.g., a knife orblade) across the face of the die at such a rate that the size range forthe dried particles is from about 0.85 to about 2.5 mm mesh. Generallythis means a rate in excess of about 500 cuts per minute, and usuallyover 1,000 or over 1,500 cuts per minute. The rate of cuttingnecessarily is rather high to achieve the small particles required, butpreferrably is kept within bounds to avoid excessive die wear. Thecutting rate also depends on a reasonable and commercially practicablelinear extrusion rate. A minimal practical extrusion rate generally willbe in excess of about 1,200 mm/min, and usually over about 1,500 mm/min.Illustratively in tests of the invention, a four-blade cutter wasrotated at 360 rpm to effect 1,440 cuts per minute across the face ofthe die having openings of 1,219 mm and a linear extrusion rate of about1,600 mm/min.

The cut and dried extrudate at a magnification of 12 times (FIG. 1) hassubstantially smooth opposing exterior surfaces 100 and 102 (see FIG.1a) in generally parallel relation. These substantially parallelopposing surfaces 100 and 102 are at opposite ends of a very short stubbody (e.g., a stub cylinder) having substantially smooth side exteriorsurfaces 103. The side surfaces 103 are angularly connected to theopposing surfaces to form angular projecting edges. The angle isapproximately 90°, i.e., a right angle 104. Particle shapes varying fromthe ideal are possible, but some key features are important, namely thatthe particles under a magnification of 12 times must have substantiallysmooth surfaces on the exterior thereof, plus angularly projecting edgeson the exterior thereof (such as formed at the 90° angles of connectionbetween opposing and side surfaces). More specifically, the particlesunder a magnification of 12 times preferably have (i) substantiallysmooth opposing exterior surfaces in generally parallel relationship and(ii) substantially smooth side exterior surfaces extending between andangularly connected at about 90 degrees to the opposing surfaces and(iii) a distance between the opposing surfaces no greater than thegreatest linear dimension of the particle in directions parallel to theopposing surfaces. That greatest linear dimension in directions parallelto the opposing surfaces is not in excess of 180% (preferably not over150%) of the shortest linear dimension parallel to the opposing surfaces(as, for example, when non-circular die openings are employed). Thecombination of these characteristics--especially the combination of thesubstantially smooth surfaces (such as, for example, formed by extrusionand cutting) and the angularly projecting edges (such as, for example,formed at the 90° angle of connection between surfaces)--surprisinglygives traditional couscous mouthfeel. Dimensions perpendicular toopposing surfaces should not be substantially greater than the maximumlinear dimension parallel to opposing surfaces. Ideally, the shortestlinear dimension is perpendicular to the opposing parallel surfaces, andpreferably is not less than 0.5 mm. Generally, the shortest lineardimension will fall in the range between about 30% and 70% of thegreatest linear dimension parallel to the opposing surface of theparticle. The distinctive new particles are shown in FIG. 1 and are tobe compared to the prior art couscous agglomerated particles of FIGS. 2and 3.

The particles formed by extrusion maintain their integrity under normalhandling conditions. They are not easily friable and do not break downinto fragments when hydrated during preparation for consumption. Theyhave a highly compacted (i.e., extrusion-compacted) and densecomposition. The composition is substantially uniform throughout theparticles, and the particles are substantially translucent, allowing thepassage of light through them in a relatively uniform manner, which istotally different from the interference to light passage exhibited byagglomerated couscous particles. The agglomerated particles have voids.They are not compacted; and while they are partially gelatinized, theyare opaque to the passage of light.

In specific experiments, durum wheat semolina blended with 0.75% byweight glyceryl monostearate (tradename "Myvaplex") as a surfactant wasfed into a preconditioner at the rate of 68 kg/hr. Water was metered inat the rate of 10.0 kg/hr, and steam at about 5 bar (80 psi) wasinjected along the bottom of the preconditioner at a rate of about0.26-0.29 kg/min No effort was made to elevate pressure beyond ambientatmospheric pressure. The mixture exiting the preconditioner indifferent test runs was at a temperature of about 93° C. to 99° C. andmoisture levels of about 26% to 28%. The conditioning cylinder shaftswere operated at a speed of 100 rpm to provide a retention time of 1.5to 2 minutes. Four conditions of extrusion following the preconditioningsteps are now set forth in table form:

    ______________________________________                                                     Example                                                          Item           1       2        3     4                                       ______________________________________                                        Extruder Shaft Speed                                                                         160     120      140   160                                     RPM                                                                           Extruder Water 9.3     7.1      4.6   9.3                                     (kg/hr)                                                                       Extruder Steam 0.184   0.175    0.170 0.273                                   (kg/min)                                                                      Vacuum (Bar)   0.33    0.33     0.33  0.33                                    Load Required (KW)                                                                           3.8     4.9      4.9   4.2                                     Temp Head 3 (Celsius)                                                                        88      100      100   97                                      Temp Head 4 (Celsius)                                                                        100     109      122   119                                     Temp Head 5 (Celsius)                                                                        98      106      110   106                                     Temp Head 6    Vent    Vent     Vent  Vent                                    Temp Head 7 (Celsius)                                                                        86      89       96    89                                      Temp Head 8 (Celsius)                                                                        91      91       97    93                                      Temp Head 9 (Celsius)                                                                        86      85       85    85                                      Pressure Head 7 (Bar)                                                                        23.8    37.4     37.4  27.2                                    Pressure Head 8 (Bar)                                                                        64.6    74.8     71.4  68.0                                    Pressure Head 9 (Bar)                                                                        68.0    81.6     85.0  68.0                                    Pressure M Zone (Bar)                                                                        27.2    27.2     34.0  23.8                                    Starch Gelatinization                                                                        88.8    95.3     94.1  97.0                                    (%)                                                                           Water Absorption Index                                                                       4.8     5.4      5.4   5.2                                     % Moisture as Extruded                                                                       37.1    34.6     32.5  37.5                                    Total Two-Step 15      11.5     10.0  11.0                                    Rehydrating                                                                   Time (min)                                                                    ______________________________________                                    

Starch gelatinization was measured by the enzymatic method set forth byShetty, R.M., Lineback, D.R., and Seib, P.A., titled "Determining theDegree of Starch Gelatinization", published in Cereal Chemistry,May-June 1974, Vol. 51, pp. 364-375, here incorporated by reference. Thetotal starch content was determined by "AACC Method 76-11;Starch--Glucoamylase Method With Subsequent Measurement of Glucose WithGlucose Oxidase; First Approval Oct. 8, 1976; Reviewed Oct. 27, 1982,"published by the American Association of Cereal Chemists, hereincorporated by reference. Most significant is the fact that at least80% by weight and in most instances over 85% or 90% and even over 95% byweight of the starch of the mixture becomes gelatinized by the processconditions and thus rendered highly absorptive of water. This isaccomplished without significantly raising the water-solubleconstituents, and in fact causing a relative lowering of them.

The Water Absorption Index (WAI) is a useful indicator of the waterabsorption capabilities of the products of the invention. This indexrepresents the weight of a centrifuged (water-containing) gel obtainedper gram of dry sample. The method for determining the WAI is describedby Anderson, R.A., Conway, H.F., Pfeifer, V.F., and Griffen, E.L., Jr.,in an article entitled "Gelatinization of Corn Grits by Roll andExtrusion Cooking", published in Cereal Science Today, Jan. 1969 Vol.14(1), pp. 4-7, 11-12, here incorporated by reference. Couscous of thisinvention has a WAI of at least 4.7 and even over 5.0, which is believedto be unusually high and indicative of quick and thorough hydration inpreparing the product for consumption.

Another index of interest but not as widely accepted as meaningful isthe Water Solubility Index (WSI), also described by Andersen et al. inthe aforenoted article. Tests made on couscous of this invention haveindicated a WSI generally less than 4.5 and in most instances less than4.0. This indicates low formation of undesirable solubles.

The total rehydrating time in the above table refers to the total timefor rehydration of the couscous as conducted by a two-step processcombined with steaming. Couscous of the present invention is relativelyquickly hydrated and even more quickly steam cooked to a ready-to-eatcondition as compared to couscous prepared by agglomeration. Thesteaming time to prepare couscous of this invention for consumption hasbeen observed to be less than one-half the time required for steaming ofcouscous made by agglomeration. For example, products of the presentinvention were ready for consumption after two steaming times of 3minutes each, whereas a test using an agglomerated product required twosteaming times of 8 minutes each. Each steaming step for couscous of thepresent invention was preceded by a period of rehydration (at roomtemperature) such as used conventionally in preparing agglomeratedcouscous for consumption. In the first rehydration period, the couscoussample was allowed to absorb water to 60% of its weight; and during thesecond, it was allowed to absorb water to 30% of its initial weight.(Conventional rehydration involves discrete steps of limited waterabsorption.) The total time for conventional two-step rehydration andtwo-step steaming of couscous to edible condition is on the order ofabout 15-20 minutes for couscous of this invention about 10-15 minutesfor limited hydration and about 6 minutes of steaming), whereas thetotal time for conventional rehydration and steaming of agglomeratedcouscous to edible condition generally requires at least about 10minutes more.

Of even greater significance is the fact that couscous of the presentinvention may be prepared for consumption in a single hydration stepinvolving submerging it in water at 25° C. for at least 2 minutes up to6 minutes, until the couscous particles increase in weight at least to180% of their original weight by absorbing water (e.g., going from 1.0gram to 1.8 grams), and then steaming that hydrated product for up to3-4 minutes with steam at 90° C. or higher.

Still further, couscous of the present invention, when prepared forconsumption using boiling water, requires less than one-half the time ofthe agglomerated product. Product of the present invention can beprepared for consumption by adding a sample to boiling water, allowingit to simmer for 2 minutes or less and allowing it to stand withoutadditional heating for up to 2 minutes.

In general, extruded product moisture levels between about 32 and 38% byweight further enhance smoothness of texture for the end product. Lowerextrusion moisture levels tend to increase extrusion pressures and causean undesired increase in the mechanical shear action of the dough.Raising the moisture content about 40% tends to increase the risk orpossibility of a drop in quality toward a lower WAI, lessgelatinization, and some unwanted stickiness associated with cutting theproduct at the die surface. Cooking zone temperatures at or below 100°C. tend to yield end products having somewhat less starch gelatinizationand requiring longer rehydration. As temperatures in the cooking zoneare increased, most preferably into the range of 110° C. to 115° C., theend products tend to exhibit improved WAI, increased gelatinization, anda shortening of rehydration times. Generally, the higherclimate-controlled drying temperatures of 70° C. to 80° C. give improvedproduct integrity, shortened rehydration times and an overall betterquality product.

There is thus provided a new couscous product and a new method to makecouscous, namely by extrusion processing. The useful quantity of productresulting from practice of this invention is exceedingly high, even inessence 100%, with no significant fines or oversized particles.

Although couscous prepared by agglomeration techniques requires siftingand grading to separate the fine, medium, and coarse grades, no suchextra step is necessary when practicing this invention. All particlescan be directly formed to satisfy the size criteria within 0.85 mm meshto 2.5 mm mesh, with all particles of a particular batch substantiallyuniform in shape and equal in size and ready for packaging. Waste isavoided and product uniformity is achieved with fewer pieces ofequipment and fewer process requirements and therefore with greatsavings as compared to the excessive expense of the commercialagglomeration technique.

Those skilled in the art will readily recognize that this invention maybe embodied in other specific forms than illustrated without departingfrom its spirit or essential characteristics. The foregoing discussionis therefore to be considered as illustrative and not restrictive, thescope of the invention being indicated by the appended claims; and allvariations coming within the meaning and range of equivalency of theclaims are intended to be embraced thereby.

That which is claimed is:
 1. A shelf-storable couscous food productconsisting essentially of non-sticky free-flowing wheat-based particleshaving a size between about 0.85 and about 2.5 mm mesh, and having amoisture content below about 13% by weight, said couscous food productbeing relatively quickly hydratable and steam cooked without loss of itsparticulate integrity and being particularly characterized by the factthat the particles thereof are substantially translucent, have a WaterAbsorption Index greater than 4.7, and have a substantially uniform anddense extrusion-compacted composition comprised essentially of thestarches and gluten-forming proteins in a blend of, by dry solidsweight, at least about 65% up to 100% of durum wheat flour or middlingsor semolina and about 35% down to 0% of flours or middlings or farinasof cereal grains other than durum wheat, at least about 80% of the drysolids weight of said starches being gelatinized, said particles beingfurther characterized by having, when examined under a magnification of12 times, (i) substantially smooth surfaces on the exterior thereof and(ii) angularly projecting edges on the exterior thereof.
 2. The productof claim 1 wherein said substantially smooth surfaces include opposingsurfaces in generally parallel relationship and include side surfacesextending between and angularly connected at about 90° to said opposingsurfaces, and wherein said angularly projecting edges comprise the edgesformed at said angular connections between said side surfaces and saidopposing surfaces.
 3. The product of claim 2 wherein said particlesexhibit their shortest linear dimension in a direction substantiallyperpendicular to said opposing surfaces.
 4. The product of claim 1wherein the size of said particles from the largest to the smallest doesnot vary more than 1 mm mesh.
 5. The product of claim 1 wherein saidparticles are of substantially the same size and shape.
 6. The productof claim 1 wherein said substantially smooth surfaces include opposingsurfaces in generally parallel relationship and include side surfacesextending between and angularly connected at about 90° to said opposingsurfaces, wherein said angularly projecting edges comprise the edgesformed at said angular connections between said side surfaces and saidopposing surfaces, and wherein said particles exhibit their shortestlinear dimension in a direction substantially perpendicular to saidopposing surfaces and said shortest linear dimension is not less than0.5 mm.
 7. The product of claim 6 wherein the size of said particlesfrom the largest to the smallest does not vary more than 1 mm mesh. 8.The product of claim 6 wherein said particles are of substantially thesame size and shape.
 9. The product of claim 1 wherein over 90 percentof the dry solids weight of said starches is gelatinized and said WaterAbsorption Index is over 5.0.
 10. The product of claim 9 wherein thesize of said particles from the largest to the smallest does not varymore than 1 mm mesh.
 11. The product of claim 9 wherein said particlesare of substantially the same size and shape.
 12. The product of claim 9wherein said substantially smooth surfaces include opposing surfaces ingenerally parallel relationship and include side surfaces extendingbetween and angularly connected at about 90° to said opposing surfaces,and wherein said angularly projecting edges comprise the edges formed atsaid angular connections between said side surfaces and said opposingsurfaces.
 13. The product of claim 12 wherein said particles exhibittheir shortest linear dimension in a direction substantiallyperpendicular to said opposing surfaces.
 14. The product of claim 13wherein said shortest linear dimension is not less than 0.5 mm.